The present invention generally relates to a lighting device. More particularly, the present invention relates to an apparatus and a method used in a lighting device for eliminating striation in a fluorescent lamp with dimming control.
The gas-discharging lamps have been the primary lighting sources in the industrial and residential uses since their development in the 1930""s. They possess advantageous features including high color rendering, soft-visualization, and low energy consumption, etc. Today, fluorescent lamps are still commonly used.
A schematic diagram of a lighting device using a fluorescent lamp is depicted in FIG. 1. Referring to FIG. 1, a voltage source VD is fed to a fluorescent lamp 10 through a ballast 20. The capacitor CS disposed across one terminal of the electrode 12a and one terminal of the electrode 12b serves as a starting capacitor. The inductor LR connected between the other terminal of the electrode 12a and the ballast 20 serves as a resonant inductor. The ballast 20 is comprised by a series-resonant inverter (SRI) for providing high frequency (about 20 kHz to 65 kHz) driving voltage. Before igniting the fluorescent lamp 10, the inside of the fluorescent lamp 10 is not in a conduction state and thus the resonant inductor LR, the filament resistance, and the starting capacitor CS make up a series-resonant circuit. After igniting the fluorescent lamp 10, the inside of the fluorescent lamp 10 is in a conduction state, and is equivalent to resistors shunted with the capacitor CS.
In the last decade or so, versatile fluorescent lamps have been developed for improving the quality of lighting environments. Nowadays, it is the trend to develop multi-functional lamp systems with dimming control, while maintaining high power quality, to achieve a more comfortable lighting environment. High power factor correction for raising the power quality is available in lamp design. However, when utilizing low-level dimming control, a low frequency snake-like striation in the lamp due to relatively significant odd-order harmonic amplitudes of the lamp current inevitably disturbs the dimming performance. This phenomenon is depicted in FIG. 2. Inside the fluorescent lamp 10, the hot electron beam 16 is in a state similar to a standing wave; therefore, the area 18 inside the fluorescent lamp 10 presents darker illumination due to lack of electron stimulation. The periodical striation may result in the luminance unstable, flicker, deforming, deflection, and even disappearing. Besides, it may disturb the operation of the lamp and raise the lamp temperature.
The early techniques for solving the mentioned striations in the fluorescent lamp include changing the gas ingredients or the lamp geometry, modulating the lamp current with FM to be out of the resonant band, and using an FM PWM strategy to spread the lamp power in different bands which is proposed by Laskai as described in the paper xe2x80x9cA unity power factor electronic ballast for metal halide lamps,xe2x80x9d Proc. IEEE APEC""94, pp. 31-37, 1994. However, these approaches are useless for lowering the amplitudes of the odd-order harmonics in a suitable level to reduce the striations. Lately, Hsieh et al. successfully proposed strategy for breaking the striations by modulating the lamp filament current with a harmonized circuit to uniformly spread the lamp energy into every harmonic to achieve wonderful low-level dimmer, as described in U.S. Pat. No. 6,087,785, July 2000. However, this approach still causes extra power loss of the lamp due to employing large signal driving in the lamp current feedback modulation.
Keep the drawbacks of the prior art in mind, and employ experiments and research full-heartily and persistently, the apparatus and method using small signal driving for eliminating striation of fluorescent lamp are finally conceived by the applicant.
It is therefore an object of the present invention to propose a generator used in a controllable dimmer ballast of a fluorescent lamp for eliminating a striation.
It is therefore another object of the present invention to propose an apparatus used in a gas-discharging lamp with a first electrode and a second electrode for eliminating a striation.
It is therefore another object of the present invention to propose a method for preventing a light apparatus from a striation.
According to the aspect of the present invention, the generator used in a controllable dimmer ballast of a fluorescent lamp for eliminating a striation includes an interface for transforming an input signal to a first input voltage and a second input voltage, an oscillator electrically connected to the interface for receiving the first input voltage and producing a pair of complementary pulse trains, a comparator electrically connected to the interface for receiving and comparing the second input voltage with a threshold voltage and providing an enable signal, and a controller electrically connected to the oscillator and the comparator for alternately modulating the pulse train so as to eliminate the striation of the lamp.
Preferably, the generator used in a controllable dimmer ballast of a fluorescent lamp is a controllable asymmetrical group-pulse train generator (CAGPTG).
Preferably, the input signal of the generator is an adjustable voltage.
Preferably, the oscillator of the generator is a constant-duty-cycle voltage-controlled-oscillator (CDC-VCO).
Preferably, the controller of the generator is an asymmetrical-group-pulse-width-modulated (AGPWM) controller.
Preferably, the controller of the generator further provides a first and a second control signals according to the pulse trains and the enable signal.
Preferably, the fluorescent lamp further includes a first electrode and a second electrode, a starting capacitor coupled between the first and second electrodes, and a resonant inductor coupled between the ballast and one of the first and second electrodes of the lamp.
Preferably, the ballast of the fluorescent lamp further includes a half-bridge series-resonant inverter (HB-SRI).
Preferably, AGPWM controller of the generator further includes a square-wave-generator (SWG) for generating a square-wave signal, a group-pulse alternator (GPA) electrically connected to the SWG for receiving the enable signal and the square-wave signal and producing two complimentary signals, and a duty-cycle-controller (DCC) electrically connected to the GPA and the CDC-VCO for receiving the two complimentary pulse trains and the two complimentary signals and producing the first and second control signals.
According to another aspect of the present invention, the apparatus used in a gas-discharging lamp with a first and a second electrodes for eliminating a striation includes an interface for transforming an input signal to a first input voltage and a second input voltage, an oscillator electrically connected to the interface for receiving the first input voltage and producing a pair of complementary pulse trains, a comparator electrically connected to the interface for receiving and comparing the second input voltage with a given thresh threshold voltage and providing an enable signal, a controller electrically connected to the oscillator and the comparator for alternately modulating the pulse trains and providing a first and a second control signals according to the pulse trains and the enable signal, and a HB-SRI for driving the lamp according to the first and second control signals, so as to eliminate the striation.
Preferably, the oscillator of the apparatus is a constant-duty-cycle voltage-controlled-oscillator (CDC-VCO).
Preferably, the controller of the apparatus is an asymmetrical-group-pulse-width-modulated (AGPWM) controller.
Preferably, the AGPWM controller of the apparatus further includes a SWG for generating a square-wave signal, a GPA electrically connected to said SWG for receiving the enable signal from the comparator and the square-wave signal from the SWG and producing two complimentary signals, and a DCC electrically connected to the GPA and the CDC-VCO for receiving the complimentary pulse trains and the complimentary signals and producing the first and second control signals.
According to another aspect of the present invention, the method for preventing a light apparatus from a striation includes steps of providing an adjustable voltage, transforming the adjustable voltage to a first input voltage and a second input voltage, providing a pair of complementary pulse trains according to the first voltage, comparing the second input voltage to a given threshold voltage for providing an enable signal, and obtaining a first and a second control signals by means of alternately modulating the pulse trains according to the enable signal for driving the light apparatus.
Preferably, the method for preventing a light apparatus from a striation further includes a step of providing the first and second control signals to the light apparatus by means of executing a signal process to reduce a plurality of odd-order harmonic amplitudes of a lamp current and to increase a plurality of even-order harmonic amplitudes of the lamp current for eliminating the striation of the lamp.
Preferably, the first and second control signals for preventing a light apparatus from a striation are in a form of symmetrical constant-duty-cycle pulse trains when the adjustable voltage is greater than a specific level and the enable signal is in a first state.
Preferably, the second control signal for preventing a light apparatus from a striation is in a form of asymmetrical constant-duty-cycle pulse train during a first half period of a specified low-frequency-modulated period when said adjustable voltage is less than a specific level and the enable signal is in the second state.
Preferably, the first control signal for preventing a light apparatus from a striation is in a form of asymmetrical constant-duty-cycle pulse train during a second half period of a specified low-frequency-modulated period when the adjustable voltage is less than a specific level and the enable signal is in the second state.
Preferably, the adjustable voltage for preventing a light apparatus from a striation is ranged from 0 to 10 v.
Preferably, the specific level for preventing a light apparatus from a striation is 5 v.
Preferably, the first state of enable signal for preventing a light apparatus from a striation is 0.
Preferably, the second state of enable signal for preventing a light apparatus from a striation is 1.